Immobilization of tissue iron on calcareous soil: differences between calcicole and calcifuge plants

Deficiency of P and sometimes of micronutrients; especially Fe, is of importance to the calcicole-calcifuge behaviour of plants. Calcifuge species are unable to solubilize these elements or keep them metabolically active in sufficient amounts on calcareous soils. To demonstrate if calcicole, calcifuge and 'soil indifferent' species differ in Fe nutrition dynamics, samples of such species were transplanted on a slightly acid silicate soil (pH BaCl2 ca 4.0) and on a calcareous soil (pH BaCl2 ca 7.2). Plants were grown in a computer-controlled greenhouse at a soil moisture content of 50-60% water holding capacity and with additional light (ca 160 mu E s(-1) m(-2), 12 h d(-1)) if ambient light was < 120 mu E s(-1) m(-2). The calcifuge species developed chlorosis when grown on the calcareous soil, whereas the other species did not. Calcareous-soil grown plants had less 1,10-phenanthroline extractable Fe in their leaf tissues than the silicate-grown plants whereas total leaf Fe showed more species specific properties. The ratio of 1;10-phenanthroline extractable to total Fe in the leaves was significantly lower in the calcifuges than in the calcicoles when grown on the calcareous soil. 'Soil indifferent' species did not differ much from the calcicoles. Root Fe, fractioned as DCB extractable 'plaque' on the root surface and Fe remaining in the root after DCB extraction, showed no distinct pattern of DCB-Fe related to the different categories, but remaining root Fe tended to be lower in the calcifuges compared to the two other categories. Leaf colour estimated by a colour scale correlated well with chlorophyll a + b content measured in the leaves of two calcifuges. Leaf P concentrations did not differ between the different categories but were more species dependent. We conclude that chlorosis in calcifuge species is related to an immobilization of Fe in physiologically less active forms in the tissue, if plants are forced to grow on a calcareous soil, whereas calcicole and 'soil indifferent' species are able to retain a much higher share of their leaf Fe in metabolically active form. This probably decreases the vitality and may exclude calcifuge plants from calcareous soil. We consider this property, previously almost unconsidered in an ecological context, as important to the calcifuge-calcicole behaviour of plants.